A hybrid between hardcore punk and thrash metal, later on including influence from death metal, industrial and noise.

A good description of Grindcore can be found on RYM, but Grind is described there as:
"A lightning fast tempo of distorted chromatic guitar riffs played over relentless blast beats accompany vocals that consist mainly of unintelligible shrieks, growls, and barks. Grindcore songs typically attack in short, ultra-violent blasts of noise, in some cases lasting only a matter of seconds, with no readily apparent song structures. Grindcore bands attempt to represent the nihilism and decay that they sense in society through this extreme music, and angry lyrics that commonly speak of social and political issues."